1. Field of Endeavor
The present invention relates to the field of rotating electrical machines. It relates to an air-cooled motor-generator as well as to a method for the operation thereof.
2. Brief Description of the Related Art
Air-cooled motor-generators are generally cooled via a closed air circuit. The required quantity of air is determined by the losses to be dissipated. Since both the losses which occur and also the generated cooling air volume flow cannot be determined precisely in advance, it is necessary to include reserves with respect to the volume flow in the planning. An excessively low quantity of air results in overheating of the generator. An excessively high volume flow results in unnecessary losses with respect to the ventilation. The aim is therefore to select the cooling air volume flow to be as high as is necessary but also as low as possible. In general, the volume flow is limited by artificially generated pressure drops within the air circuit (throttle principle).
Devices and methods embodying principles of the present invention can simplify and optimize this procedure. The aim is to match the cooling air volume flow to the requirements for cooling as precisely as possible, whether this be once, when generators are first brought into operation, or more often, in the case of different load cases of the generator, such as arise in the case of asynchronous machines. Conventionally, this is brought about, for example, by constricting specific cross sections within the air path in the case of water-powered machines, as are disclosed, for example, in FIG. 1 of document EP 740 402 A1. In the case of large water-powered machines, this often takes place at the inlet to the rotor spider. By virtue of additional laminations, the inlet cross section is constricted and therefore the quantity of cooling air is limited.
However, this procedure has a few disadvantages:                It is no longer possible for the covering laminations to be mounted on the rotor spider, depending on the construction of the machine with the installed rotor. The opening area at the inlet to the rotor spider therefore needs to be fixedly defined even before the rotor is installed.        If the introduction of additional laminations is possible with the rotor installed, this can also only take place when the machine is at a standstill. This is time consuming and, nevertheless, the volume flow cannot be influenced precisely.        The covering laminations increase the weight with which the bearings are loaded. Furthermore, the laminations need to be fixed correspondingly carefully since they are located on the rotating part of the generator.        The volume flow distribution, which is decisive for the uniformity of the cooling and therefore the temperatures in the machine, can be negatively influenced.        It is not possible to respond to different load cases of the generator.        